Integrated Regional Information Networks | July 26, 2010
Stem rust has been confirmed in South Africa. It had been controlled for decades, but is back and spreading.
Stem rust is a fungus which kills wheat. Resistant wheat varieties were developed and planted widely. But the fungus mutated. In 1999, a new strain named Ug99 was found in Uganda.
The strain quickly spread to Kenya, Ethiopia, Sudan, Yemen, Iran and South Africa. New forms of Ug99 that infect rust-resistant wheat have been identified in some of these regions. Professor Zak Pretorius is a wheat pathologist at the University of the Free State in South Africa. “It was alarming for us that one of the resistant genes was not effective anymore,” he says. Smallholder wheat farmers are at risk, as scientists race to develop varieties that are resistant to the new strain of Ug99.
Stem rust can be identified by rust-coloured patches on the stem and infected parts of the plant. It is spread by spores that are usually transported by wind. Spores can survive harsh winters. They germinate in warmer conditions. They can be carried on clothing and can travel long distances, including between continents.
Fungicides can control Ug99. But they are often too expensive for small-scale farmers. Peter Njau is a research scientist at the Kenya Agriculture Research Institute. He says that during the 2003 epidemic, an anti-fungal chemical was recommended, with hopes that the pathogen would be eradicated.
“But instead, it worsened” says Njau, “…because most farmers, especially smallholders, could not afford it.” The chemical cost 37 dollars a litre. It had to be sprayed three times a season.
Aston Kirui is a Kenyan wheat farmer from Katakala village in Narok. He lost most of his crop in 2009 to Ug99. His field escaped this year. But his neighbour was not so lucky. “I have a neighbour who is going to lose everything this year. His farm looks like a field in an arid area during drought,” Mr. Kirui says. “I am shocked that you are telling me that there is a new strain that has more resilience. I did not know about it.”
Ayichiluhim Mojo is a wheat farmer in Ethiopia. He has frequently lost his harvest to wheat stem rust over the past decade. “But I don’t know anything about the new types of wagg,” he says, using Ug99’s local name. Negussie Gemechu is Head of the Wereda Agriculture Bureau. He said he has not yet heard about the mutant Ug99 and there have been no major wheat losses recently. Mr. Gemechu says, “The sowing season for wheat is yet to come. But in the incident of any wagg, we will alert our farmers.”
So far, wheat rust has not caused the disaster that scientists fear. The safest way to prevent that disaster is to continue to develop varieties that are resistant to stem rust. “We will now have to make sure that every new wheat variety we release has iron-clad resistance to both Ug99 and the new races,” says Ravi Singh, senior scientist in plant genetics and pathology at the International Maize and Wheat Improvement Centre.
The next challenge is to get the new varieties into small-scale farmer’s fields quicker than Ug99 can spread.